xfstests: optionally run all tests under quota

xfstests: optionally run all tests under quota

This patch might be a little heavy handed, but it seems to
work; if you set USE_QUOTA=1 in your environment, all
tests should be run with quota on and enabled.

This will hopefully help shake out some of the ext4
quota problems, although one needs to keep an eye
on the console to see whether warnings scroll by.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>